In Vitro Phagocytosis by Molluscan Hemocytes: A Survey and Critique of Methods

Abstract

Endocytosis is a widespread cellular function in which vesicles and vacuoles formed by the plasma membrane regulate the uptake of molecules in a cell’s environment. Most eucaryotic cells have this function; however, among mammalian cells, in which it has been mostly thoroughly studied, it is most prominent in leucocytes, ma-crophages, capillary endothelial cells, thyroid epithelial cells, yolk sac cells, and oocytes (Silverstein et al., 1977). Endocytic activity is usually divided into two categories. Phagocytosis, or “eating”, is used to describe the uptake of large particles. This uptake occurs by close apposition of a segment of the plasma membrane to the particle’s surface, while excluding most, if not all, of the surrounding fluid (Silverstein et al., 1977). Particle size has been described as having the range of 0.01 μm to 10 μm and may include microorganisms (from viruses to bacteria and fungi), as well as inert particles (Cohn, 1972). The term pinocytosis, or “drinking”, is used to describe vesicular uptake of everything else. This may include small particles (such as lipoproteins, ferritin, colloids, and immune complexes), soluble macromolecules (e.g., enzymes, hormones, antibodies, yolk proteins, and toxins), and low molecular weight solutes. It is assumed that uptake of extracellular fluid is always included in pinocytosis (Silverstein et al., 1977). Since little information exists on in vitro pinocytosis in molluscan hemocytes, aside from the work of Feng (1965), this discussion will focus on that part of the endocytic process termed phagocytosis for which more information is available.